Temperature Dependence of Deformation Behavior in Magnesium and Magnesium Alloy Single Crystals

Abstract:

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It is important to research activation of the slip systems in magnesium crystals to
understand deformation behavior of magnesium. In this study, pure magnesium, Mg-7.0at%Li and
Mg-0.1at%Zn single crystals were stretched in the [11-20] direction in the range of 77K to 573K to
investigate the deformation behavior by non-basal slip. The active slip system was investigated by
the observation of slip bands, etch pit bands and dislocations by TEM. {11-22} second
order pyramidal slip is activated in all magnesium and magnesium alloy single crystals, and its yield
stress shows anomalous temperature dependence in the range from 77K to 293K, however, the
yields stress decreased rapidly with increasing temperature above 293K. The yield stress due to
the pyramidal slip in Mg-Li and Mg-Zn alloy were lower than that of pure magnesium about 20MPa
whereas the stress of Mg-Zn at 77K was about two times higher than pure magnesium.

Abstract: This paper deals with the effect of temperature on plastic buckling strength of cylindrical pipe of some magnesium alloys subjected to shot peening process. Workpieces are three cylindrical pipes of AZ31, AZ61 and AZ80 magnesium alloys. The shape of pipe is 30mm in height, 16mm and 14mm in outer and inner diameters. The shot peening treatment was given on the surface of cylindrical pipe using an air-type peening machine. Plastic buckling strength test was performed under axial compression in a case of both ends with fixed condition, at several temperatures between 293K and 573K and at a crosshead speed of 1 mm/min using an Instron-type testing machine. From the experimental result, buckling stresses for all kinds of AZ31, AZ61 and AZ80 alloy pipe were strengthened after the shot peening treatment, but a few of differences for the increasing ratio. The buckling stress of the shot-peened pipe was kept higher than that of as received one up to the test temperature of 473K, however it tended to be around equal at 573K.

Abstract: Magnesium alloys have been increasingly used in automobile, aerospace, consumer electronics and communication industries due to their low density, high strength to weight ratio, good impact resistance and castability. Impact situations in vehicles and airplanes and high speed metal working are characterized with the high rates of loading. The dynamic properties of materials are critical to evaluate the materials’ response in impact situations. They are also useful to design various automotive and aerospace components that are subjected to high rates of loadings. In current study, the compressive behaviour of magnesium alloy AZ31B has been examined over a wide range of strain rate between 103 and 3x103 s-1 in order to evaluate its potential in structural applications. Higher stresses are observed at higher strain rates. The peak stress increases about 10% for an increase in the strain rate from 980 s-1 to 2450 s-1. The hardening exponent n increases from 0.65 to 0.72 with increasing strain rate from 980 s-1 to 2450 s-1 indicating that the alloy is rate sensitive. However, the rate sensitivity of the alloy is negligible at lower strains and is significantly higher at higher strains. Energy absorption during deformation in general is increased with the strain rate.

Abstract: One of the ways for determination of flow curves is the application of a ring test. Using this method, friction in the interface between the die and the specimen leads to a bulging of the sample and thereby to an inhomogeneous stress and strain state. The calculation of the flow stress from experimentally determined force–displacement curves implies a uniaxial stress state, but this will produce an error because of the above-mentioned bulging, when friction occurs. One method of avoiding these sources of error is to use the sigmoid curves, but the sigmoid curves are varied by the change of temperature and strain rate. Calculations of numerical sigmoid curves were done by the use of an iterative procedure, applying a corrective function. The paper presents a complete investigation of the AZ41 magnesium alloy sigmoid curves at temperature ranging between 473 K and 513 K and strain rates ranging between 0.025 s-1 and 0.00025 s-1 . Ring tests are used to determine the numerical sigmoid curves sensitivity to temperature and strain rate.

Abstract: In this paper, according to the characteristics of the sheets of poor plastic at room temperature and good plastic which is significantly increased after heating, the mechanical properties, microstructure evolution, the flow stress, plane anisotropy and fracture mechanism of AZ31 magnesium alloy sheets at high temperature are studied and analyzed, which provide a reliable basis for the stamping processes of the sheets at high temperature. The most suitable heating temperature for deep drawing sheets of AZ31 magnesium alloy are achieved by the hot-stamping test, and the most suitable heating temperature are near to 350°C. The results for the improvement of the hot-formability of AZ31 magnesium alloy sheets at high temperature provide a theoretical basis and new method.

Abstract: Lightweight materials have been in focus in recent times for their use in automobiles, planes and protective structures for numerous benefits ranging from reduction in fuel consumption and increased payload in vehicles to lighter and stronger protective structures. For efficient use of materials in applications where they are subjected to unusual higher sudden loads, it is necessary to understand their mechanical behaviour under such conditions.In present study, the effect of strain rate on deformation of magnesium alloy AZ31Bunder compression has been investigated. The alloy is subjected to various strain rates as 10-4s-1, 500s-1 and 2500s-1 and the microstructural analysis was performed to see the changes in the microstructure of the alloy and their effect on the mechanical response of the alloy is portrayed.